Conventionally, a band-gap circuit has been known as a circuit for generating a reference voltage having no temperature dependence. The band-gap voltage generated by the band-gap circuit is 1.2 V or so under normal circumstances. However, Japanese Patent Application Laid-Open No. 2002-318626 discloses the band-gap circuit of 0.5V or so as the band-gap circuit operable at low supply voltage. As shown in FIG. 1, it creates, in different circuit blocks, a PTAT (Proportional To Absolute Temperature) current having a characteristic proportional to an absolute temperature at a positive gradient and a CTAT (Complementary To Absolute Temperature) current having a characteristic dependent on the absolute temperature at a negative gradient, respectively. These currents are added to generate the current having no temperature dependency, and the current is passed through a resistance of an output portion so as to convert the current to a voltage and create a low reference voltage having no temperature dependence.
In such a circuit, a current source transistor is operable even in the case of a low supply voltage. In the case of this circuitry, two feedback control amplifiers and five current paths are required.
The band-gap circuit wherein the PTAT current and CTAT current are created in the same current path and the low reference voltage is thereby created with only one feedback control amplifier and three current paths is shown in “Hirofumi Banba et al, ‘A CMOS Band-Gap Reference Circuit with Sub 1 V Operation’ 1998 Symposium on VLSI Circuits Digest of Technical Papers, p. 228 to 229.”
In these conventional techniques, it is necessary to add the PTAT current and CTAT current and pass it through a third current path to convert it from the current to the voltage. The current passing through the third current path is influenced by a change in VDS of a MOS transistor for mirroring the current when the noise from power supply is added. A current value changes due to this influence, and PSRR deteriorates. Therefore, there is a problem that the PSRR and noise characteristic are worse than a typical 1.2 V output band-gap circuit. In addition, there are a large number of current paths, and so the number of elements as a whole increases and the noise and reference voltage variation amounts deteriorate.
An object of the present invention is to provide the band-gap circuit operable at the low supply voltage and capable of generating the low reference voltage, which further has high PSRR, low noise and few reference voltage variations.